The present invention relates to an improved chuck for gripping a tool bit or the like and, more particularly, to an improved self-tightening chuck in which a tool bit can be inserted from one end through a tool receiving opening or from the other end through a central cannula and in which the gripping force applied to the tool bit increases with the torque applied through the chuck.
Various drill chucks are known for releasably gripping a tool bit such as a twist drill. The most common drill chuck in use is the Jacob-type chuck used on portable electric drills. This chuck includes wedge-like jaws located in a nosepiece with the jaws adapted to converge on and tighten about the stem of the tool bit. The chuck includes a cylindrical adjusting sleeve that is rotated relative to a chuck body to effect tightening. This sleeve typically includes axially extending teeth that are adapted to cooperate with a separate gear-type tightening key to effect tightening and loosening of the chuck. While the performance of the Jacob-type chuck is generally satisfactory in industrial and consumer applications, the separate tightening key requires a minimum level of mechanical skill on the part of the user and also requires that the tightening key be kept available for use on an as-required basis.
When adapting a Jacob-type chuck to medical applications, for example, for use on portable electric drills used in orthopedic surgery, the requirement for the separate tightening key increases the number of manual manipulations that must be performed by the surgeon during the operation and increases the burden on the nursing assistant who is responsible for the various surgical instruments. The extra manual manipulations are especially burdensome when inserting long pins or wires of indeterminate length into bone and tissue to permanently reinforce the bone structures or to secure bone fragments in place during the healing process. When inserting wires into bone and/or tissue, the wire is usually loaded into the surgical drill through a central cannula or passage and is tightened in the chuck with a short segment of the wire extending axially outward from the chuck. After this first short segment is inserted in place, the chuck is loosened and the drill retracted another short segment along the wire and retightened with this second segment then inserted. This insertion sequence, including the manual tightening and loosening steps, is repeated until the desired length of wire is in place. As can be appreciated, the tightening and loosening steps required for the insertion of each short segment increases the number of manual manipulations that must be performed and is especially burdensome when a large number of long wires must be inserted to secure bone fragments into place.
Various drill chucks, known as self-tightening chucks, have been designed in an effort to eliminate the need for the tightening key. These chucks have included gripping jaws or elements that cooperate with cam surfaces to self-tighten on the drill bit and have included gripping jaws which toggle to increase the gripping force. While these types of self-tightening drill chucks have been generally satisfactory for industrial and consumer applications, they are not particularly suited for orthopedic applications. For example, the ratio of the range of adjustment, that is, the ratio of the largest to the smallest tool bit diameters that can be accepted by these prior chucks is such that they cannot accept both the small-diameter reinforcing wires and the larger diameter pins commonly used in orthopedic applications. From a practical standpoint, these prior chucks are typically fabricated by press or shrink fitting the various parts together to form a permanently assembled unit. From a medical standpoint, this type of fabrication prevents convenient disassembly of the chuck for cleaning purposes.